Related fields include thin-film microwave devices with superconducting components.
At temperatures<100 mK, amorphous silicon (a-Si) is a dielectric. Its low cost and ease of fabrication make it attractive as an interlayer dielectric (ILD) for superconducting interconnects and components for planar microwave devices, but its loss tangent (˜108) is much larger than that of single-crystal Si (˜107) at microwave frequencies (e.g., 3-300 GHz). The loss tangent is believed to be caused by defects occurring during deposition.
ILD films are typically tenths of microns thick (e.g., 300-500 nm). At this thickness, many surface treatments are ineffective to remove defects from the bulk of the film. This is also an inconvenient thickness to form by the precisely controlled methods of atomic layer deposition (ALD); because each ALD cycle creates a monolayer on the order of 0.1 nm thick, a layer hundreds of nm thick would take too long to be cost-effective.
Hydrogenation has been observed to improve a-Si loss tangent in some cases. However, only hydrogen (H) that is strongly bonded to Si helps to reduce loss. H that is trapped in interstices of the a-Si, or that is weakly attracted to dangling bond sites of two neighboring Si atoms, can form a two-level system (TLS) that increases noise and loss. For example, early studies of Josephson-junction-based qubits for quantum computing attributed loss and decoherence primarily to extraneous TLS effects from defects in dielectrics.
Therefore, a need exists for methods to reduce the microwave-frequency loss tangent of a-Si films by reducing or eliminating defects in the bulk of micron-scale films as well as on the surface. Preferably, this method should avoid or minimize the creation of additional TLS.